Gas turbines with sequential combustion have been known in the prior art, in which the combustion gases from a first combustor, after performing work in a first turbine, are fed to a second combustor, where, with the aid of the combustion air which is contained in the combustion gases, a second combustion takes place, and the reheated gases are fed to a second turbine.
For this second combustion, SEV burners such as those described for example in “Field experience with the sequential combustion system of the GT24/GT26 gas turbine family”, ABB Review 5, 1998, p. 12-20, or in EP 2 169 314 A2 can be used.
FIG. 1 is a perspective view of an SEV burner, in accordance with the prior art. As shown in FIG. 1, the SEV burner 10 includes a mixing chamber 12 which extends in a flow direction (see the long arrows). Connected upstream to the mixing chamber 12 is an inlet 11, through which combustion gases 18 from the first combustor (not shown) can enter the mixing chamber 12 after expansion in the first turbine (not shown). Connected downstream to the mixing chamber 12 is a combustion chamber 13 in which a burner flame, with a corresponding flame boundary 17, is formed during operation. The mixing chamber 12 is outwardly delimited by means of a burner wall 15 which has a multiplicity of effusion holes 16. An angled fuel lance 14 projects into the mixing chamber 12, from which a fuel 19 is injected into said mixing chamber 12.
FIG. 2 shows a section view through the burner wall of an SEV burner with effusion cooling in accordance with the prior art. Cooling air 20 is fed on the outside opposite to the flow direction of the combustion gases 18 in the mixing chamber 12 and enters the mixing chamber 12 through the effusion holes 16 in the burner wall 15 and brings about effusion cooling (see FIG. 2). As a result of feeding the cooling air along the burner wall 15, this is convectively cooled. As disclosed in EP 2 169 314 A2, there is a desire in the case of such SEV burners to improve cooling and to prevent flashback so that the sequential burners can be operated at higher hot gas temperatures and with highly reactive fuels.
In the case of conventional burners of gas turbines as disclosed in, U.S. Pat. No. 7,493,767 B2; an impingement cooling of transition pieces, to vary and influence the distribution of cooling air over the impingement cooling plate using holes in the plate equipped with “flow capturing elements” or “scoops” to provide locally higher mass flows of cooling air. Since in this case, owing to the lack of effusion cooling, the cooling air does not enter the mixing chamber directly through the burner wall but is guided along the burner wall on the outside, no consideration has to be taken for the interaction of the flow in the mixing chamber with cooling air which flows in through the burner wall.
In the case of an SEV burner, however, there is a close relationship between the distribution of the inflowing diffusion cooling air and the flow conditions in the mixing chamber or in the subsequent combustion chamber.